Problem is the pressing game Pirlo coaches is mostly work when opponents want to attack or at later stage of the games, when opponent is tired. It is somewhat ok in CL, when teams want to attack and win. In Serie A, it is useless when teams tend to play steady, so our attack in the first half will be useless, and doing pressing game early will eat up our player's stamina. And when people is out-of-stamina, their concentration is also drop and we also make more error.
One more problem with our squad is that many of our player have poor stamina or too old to play that pressing style. Dybala, Arthur, Ramsey, Alex Sandro (he has good stamina on 2016-2017 but not now). Ronaldo (he is 35, so his stamina is not good anymore). Another set of players like Bentancur, Rabiot, Danilo have stamina to play, but all of them have problems with concentration and tend to make stupid mistake like give away ball in dangerous position. And our defence is lead by Bonucci, who will make at least one big mistake per game.